The present invention relates to a gasket for a cylinder head and, more particularly, to a gasket arranged between a cylinder block and cylinder head of an internal combustion engine.
An internal combustion engine includes a cylinder block and a cylinder head, which are fastened together by bolts. A gasket is arranged between the cylinder block and cylinder head to seal the engine against the escape of fluids, such as combustion gas, oil (lubricant), and coolant. Holes are formed in the gasket at predetermined locations to allow for the passage of the combustion gas, oil, coolant, and bolts. Various types of sealing beads are formed around the holes (refer, for example, to Japanese Laid-Open Patent Publication Nos. 4-64776, 2000-220740, and 8-285080). The beads are each formed to produce a sealing pressure that differs in accordance with the subject it seals when the gasket is fastened by the bolts. For example, a high pressure bead having a high sealing pressure is used as the bead that seals the rim of a hole (lubricant hole) through which lubricant passes from the cylinder block to the cylinder head. A low pressure bead having a low sealing pressure is used as the bead that seals the rim of a bolt hole.
The gasket uses a high pressure bead to seal a lubricant hole. Nevertheless, the gasket, which is exposed to high pressure oil and used under harsh conditions, is susceptible to wear and deterioration. When such wear or deterioration occurs, lubricant may escape from the high pressure bead, move through a gap formed between the gasket and cylinder head, and ooze out of the engine.